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Re: Xen vs VMware

From: Freddie Cash <fcash-ml@xxxxxxxxxx>
Date: Wed, 18 Oct 2006 13:47:05 -0700

On Wednesday 18 October 2006 12:42 pm, Steve Mynott wrote:
> On 10/18/06, Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx> wrote:
> >     Generally speaking I prefer the VMWare concept over the Xen
> > concept. Xen actually has to run two operating systems, one serving
> > as the master and the other as the 'guest' OS, and this compounds the
> > number of potential bugs you might run into a lot more then a machine
> > emulator does.
> I'm surprised by this.  Xen (abstracting out some sort of meta
> operating system) seems a "cleaner" and simplier solution to me than
> running a  complex software copy of real hardware.
> Anyway aren't we just talking about lines of C in both cases?  I
> suspect the number of bugs in either would just be a function of the
> total lines of C.
> Xen is relatively small.   Although vmware source, isn't available
> AFAIK would anyone care to estimate lines of source for it?

Xen itself is small.  However, every OS that you want to run on top of Xen 
needs to be made Xen-aware, with a custom kernel that uses Xen features.  
For that reason, you can really only run open-source OSes on top of Xen 
right now.  You also lose the ability to query the hardware 
(lspci/pciconf for instance return empty statements on Xen) from within 
the guest OS.

VMWare emulates a full PC, with a BIOS and everything.  You can run any OS 
on top of VMWare, without changing the OS in any way.  Everything runs 
the same as if it were installed on real hardware.  You can even query 
the virtual hardware using things like pciconf/lspci.

With the new CPUs from Intel/AMD that include hardware virtualisation 
features, it is theoretically possible to run any OS on top of Xen 3.0+, 
but I have not heard of anyone successfully doing that as yet (not that 
I've searched all that hard).

Xen's para-virtualisation method is said to be a lot faster than VMWare 
full virtualisation method.  With support for hardware virtualisation 
features in newer CPUs, VMWare's latest products are supposedly almost as 
fast as Xen.  And they've started using a few para-virtualisation tricks 
as well to speed things up.

Basically, it boils down to whether you want a virtual OS or a virtual PC.  
Xen is the former, VMWare is the latter.
Freddie Cash, LPIC-2 CCNT CCLP      Helpdesk / Network Support Tech.
School District 73                  (250) 377-HELP [377-4357]
fcash@xxxxxxxxxx                    helpdesk@xxxxxxxxxx
Freddie Cash, LPIC-2 CCNT CCLP      Network Support Technician
School District 73                  (250) 377-HELP [377-4357]

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